Field of the Invention
The invention relates to a multicolor rotary printing machine for printing sheets or webs, having on-line register adjustment, or register measuring devices. The invention serves for determining register deviations between different ink colors, especially deviations in regard to circumferential, side and diagonal register, which are to be minimized with register adjusting devices connected with a steering and control device.
The known art includes a stationary installed photo-electric scanning device for register marks, which is connected with a switching device for measuring register mark positions (DE 32 26 078 A1, DE 26 43 481 A1, DE 27 31 914 A1, DE 26 58 659 A1, DE 40 14 706 A1, and DE 40 14 708 A1).
The times between the register signals are evaluated between each other or in response to a reference signal, wherein the time/path relations of position deviations of the register marks can be evaluated. In the known devices, the scanning arrangement is connected with start/stop inputs of a counter circuit, whose counting state is proportional with the timed appearance of reference signals and register mark signals (DE 32 26 078 A1). As reference signal, it is possible to use, for example, a fixed edge on a cylinder transporting the printed material, which is detected by means of a scanning device. The known art has the drawbacks that the velocity of the printing material must be constant, which in practice cannot be assured. The peripheral velocity of a printing cylinder swings back and forth even at a constant printing speed as much as several tenths of a percent, which leads to an impermissibly high error in the measurement of the register marks when the register marks are sensed by the scanning device on the surface of the printing cylinder. The uneven velocity is a result of variations in the load on the printing machine drive since the load during printing is subject to strong variations both in regard to time and in regard location in the machine.
Furthermore, there are known devices by means of which the angular position and velocity of a cylinder transporting printing material can be measured with incremental or absolute angle transmitter (DE 26 58 659 A1, DE 27 31 914 A1).
In that manner, the appearance of the register marks are evaluated in relation to the angular position of the cylinder, and from which the actual deviation of a register mark can be determined on the basis of the sheet length in the form of a nominal value. In that case incremental angle transmitters are used, for generating a specially generated reference or zero pulse, which is used as a reference for the angular position at which the register mark signal appears.
Such angle transmitters for determining register deviation require additional investment, especially since the angle transmitter requires a certain mounting space and must, for the purpose of measurement, be mounted very precisely. Furthermore, the transmission of the measuring signals from the angle transmitter require additional electronic investments in order to assure high validity of the signals in the presence of noise. The measurement of the position of the register mark with angle transmitter is subject to error, since during the printing, especially due to forces caused by the gripper and forces appearing during and after the print slot in the printed material (i.e. the point of contact between superimposed rollers or cylinders or printing cylinders and forms), and at least in subregions a relative movement relating to the surface of the transporting cylinders, which can cause errors in the register signals relating to the angle transmitter signals.
In the European Patent application EP 04 44 583 A2, there is described marks printed on a printing material for determining registration, which include crossing lines visually printed for each print color, and which include a linear and a curved section which are machine-readable. The visual sensing of the register deviations is performed in economical off-line manner by means of an optical register cross reader. The machine sensing is performed by means of a video camera, by means of which scanning signals serve to control register adjusting devices.
The aforesaid method has the drawback that for on-line precise register adjustment the data for machine evaluation must be present in predetermined mutually separate positions on the printed material, which requires a relatively wide section of the printed material for the register marks, and require a photo-electric sensor matched to the register marks, and has a scanning width adjusted to the width of the register marks. Furthermore, this approach does not provide information as to which reference the measurements of the register deviations are related.